Bone-conduction hearing-aid



June 23, 1936. s. Y. WHITE BONE CONDUCTON HEARING .'AID

Filed May 24, 1953 C /t 3Y IQ IO 1 CL b,

(/I l 2X C SMT ATTORNEY IENTOR BY 5. V, wht:

Patented `lune 23, 1936 UNITED STATES PATENT OFFICE 2,045,427 BONE-CONDUCTIoN HEARING-Am Sidney Young White, New York, N. Y., assignor, by mesne assignments, to Sonotone Corporation, New York Application May 24, 1933,

York, N.Y., a corporation of New Serial No. 672,534

4 Claims. (Cl. 179-407) This invention relates to bone-conduction heartion will be best understood from the following.

description of embodiments thereof, reference being had to the accompanying drawing, wherein Fig. 1 is an end View of a Rochelle salt crystal; Fig. 2 is an elevation of a plate-shaped crystal member cut from the crystal in Fig. 1;

` Fig. 3 is a side view of the plate of Fig. 2;

Fig. 4 is a View of the bone vibrator of the hearing-aid device as worn by a person using it;

Fig. 5 is an enlarged longitudinal sectional view of one form of the new vibrator;

Fig. 6 is a front view of the bone vibrator with the front cover removed;

Fig. 7 is a vertical sectional View through the crystal vibrator unit of Figs. 5 and 6;

Fig. 8 is an elevational view of the vibrator unit;

Figs. 9 and 10 are views similar to Figs. 5 and 6 of a modified form of the invention; and

Figs. ll and vl? are views similar to Figs. 5 and y 6 of a still further modification of the invention.

Fig. 13 is an elevational view of the vibrator unit mounted on a lorgnette handle.

It has been known for many years that a large percentage of deafened persons suffer only due to impaired middle-ear or outer-ear organs and that their interior auditory center is able to hear well sound vibrations conveyed thereto by boneconduction. This was proven in early experiments by pressing one end of a sound conducting rod of wood against a bony part of the head, or preferably against the teeth, while the other end was placed against a musical instrument and thus imparting musical hearing sensations to an apparently deaf person. Experiments were also made in imparting hearing `by fans ofv fibre or similar materials exposed to sound vibration and placed at one end between the teeth of the listener.

Many efforts have been made in the past to ap-4 ply apparatus of the type developed in the telephone art for bone-conduction hearing-aids. More recently, there have been devised bone-conduction hearing-aids in which a microphone that converts sound waves into electrical oscillations was made'to supply amplified oscillations to .an

` tory center.

tric substances, such as electromagnetic bone vibrator and to impart therewith corresponding mechanical vibrations to the bone structure of a listener with suilicient power to induce hearing sensations in this audi- Such electromagnetic vibrators are 5 relatively complicated in construction and usually require a large conspicuous structure for imparting the required mechanical vibrations to the bone structure.

'I have found that vibrators made of piezo-elecl0 Rochelle salt crystals, are ideally suited for bone-conduction hearingaids and enable sufiicient and faithful reproduction of sound by bone-conduction in a way suvperior to' the devices known in the past.

The principal piezo-electric substances known at present are the'crystals of quartz, tourmaline and Rochelle salt, such crystals exhibiting deformation of their structure on being subject to an electric eld, and generating an electric fieldon beingsubject to externalpressure. Rochelle salt crystals and portions thereof give a much greater deformation under the same electrical conditions than the other substances.

A Rochelle salt crystal as shown in an end view ln Fig. 1 is usually of the orthorhombic type and has a longitudinal optical axis c (perpendicular to the plane of the drawing), a major transverse axis b, usually perpendicular to two opposite prismatic surfaces of the crystal, and a minor transverse electric axis a, perpendicular to the two other axes. A rectangular plate l0, as shown in Figs. 2 and 3, cut in longitudinal direction from such crystal, with its planes perpendicular to the electric axis a, will, upon application of a potential difference to electrode sheets Il, l2 attached to the opposite at crystal surfaces I3, expand in a direction :n inclined to the optical axis c, while contracting in the diametrically opposite direction which is 90 displaced against the di- 40 rection a: of the expansion. The directions of the expansion and contraction reverse upon reversal of the polarity of the potential difference. By cementing two such oppositely oriented crystal plates to each other into a unit and applying 45 proper potentials to their surfaces, one pair of the diametrically opposed corners of the complete unit will bend forwardly while the other pair of corners will bend rearwardly.

Such unit, called a twister, will twist in one or the opposite direction depending on the polarity of the potentials applied to the flat surfaces thereof and will perform twisting vibrations when the electrode sheets on its surfaces are connected to a source of alternating potential. A crystal vibrator unit of this type, Ill/e x 21/2 x 3A," in size will tudinal direction upon application of a potential when connected to a source of sound-frequency diierence to the ilat surfaces on the two crystal currents, for instance, to an amplifier output cirsides, and will contract upon application of a recuit of a radio receiver, vibrate in accordance with versed potential to said two surfaces.

the impressed electrical oscillations. Upon press- By cementing two such crystal strips 2l and 22 5 ing a portion of the crystal against the mastod f Opposite Orientation t0 each other so that on bone or other portion of the bony structure of the application of an electric eld, one of them tends head, such vibrating crystal unit will transmit to expand while the other contracts, the cemented corresponding sound vibrations over the bones unit will be bent either in one 0r in opposite dilo of the head to the inner auditory center of the rection over adistance much larger than correl0 person and induce hearing sensations correspond- SDOflding t0 their lOIlgitlldllal eXDaDSiOn and C011- ing to the impressed vibrations. It will faithfully tlfiCtOn, in a Way Similar t0 the bending 0f a reproduce music and speech and will enable per. bimetallic thermostat having two metal strips of sons with impaired outer and middleear Organs different linear coecients of thermal expansion to hear well, and serve as an excellent bone vi- Welded togethel Such Crystal VbratOr unit is 15 brator for bone-conduction hearing-aids. Called a bender- Hard of hearing persons usually seek to conceal Ill-01' der t0 apply the potentials t0 the Crystal their impairment, A hearjngld, though satisunit, an electrode layer 23 and an electrode layer factory in Operation, lwill nd only very Hmired 24,111 the form of tin foil, for instance, are secured use if it has to be Worn prominently by the user to the outer flat surfaces of the two crystals, and 20 and it distorts his appearance, thus emphasizing an additional intermediate electrode layer 25 is his impairment To be practical and nud genera] secured to the two cemented opposite inner suruse, a hearing-aid must not only be helpful in imfaces of the two crystals. It is important that the proving the hearing, bur. ll; must also be of a Smau tin -foil be placed as close as possible to the 25 size and form which renders it inconspicuous so adjacent Crystal surfaces to reduce l@ a minimum 25 lookers are noticing his impairment, crystal surface relatively large. In this way the :l0 In bene-e0nduetien hearjngids, it is best to larger part of the oscillatory potential is applied 30 apply the bone vibrator te a portion of the bone to the cli-electric material of the crystal strips, Structure of the head of the user, preferably to the losing only little of the available potential difrnasreid bone back of the ear The pezelecmc ference in the layers between the tin foil sheets twister unit described above, though it is eilicient and thoolyslal Surfacesas a sound frequency vibration transmitter, is so The tm foll'eloolll'odos 23 24 and 25 are made large that when. applied to the bone structure of Somewhat Smaller than the Crystal Surfaoos to the head as a bone vibrator, it attracts attention wllloh they are attached lo pl'ovldo an lllslllolllllg te the user and is very conspicuous distance 26 around the edge of the crystal and To avoid these difculties, the bone vibrators of Secure a lllgh leakage roslotanoe between the 'oleolo my invention are made of small crystal sections llode Surfaces 0n the Opposite Sides 0f the crystal u constructed to constitute a tiny bone-vibrator Slrlp- Potontlals are apollo@ to the lu foll elec' structure that may be inconspicuously applied to ll'odes by Small Coppel' termlllal strips 2l 28, 29

the head of the user, and yetl able to develop Suf which are joined to the tin foil sheets and extend l elenr vlbratory power for imparting to the head beyond the edges of the crystal strips, the outer bone structure the amount of yjbratory energy terminal strips 21 and 28 being joined into a com- 45 required to induce Satisfactory hearing mon terminal member 30 to apply the full avail- As shown in Figsu, 5 and 6, the bone Vibrator able potential difference to each of the crystal l5 of my invention is made in the form of a small Plates 2 l and 22, the Crystal plates being so easing ls which js held against the mastoid bone orientedthat one contracts while the other exback of the ear of the user by means of a head pands on application of such potential difference 59 band I1, the head band being readily hidden to the termlnals under the hair of the person and the casing be- The crystal unit 20 ls arranged fol' mounting ing so small that it is slbstantially fully hidden ln the oaslng lo Wllloh may bo modo of an ln* back of the een of the pers0n A vibrator unit sulating substance, such asa phenolic condensate,

in casing I 6 is supplied with electrical oscillaandls Shaped to lll; the contours of llllo Crystal- All 515 tions through a hln double conductor cord a the front sides, the casing is open and its interior which is readily hidden under the clothing of the Chamber 3l ls arranged to be Closed loy a @over person, the cord leading to a source of sound fremember 32- Tho lower portion of the Casing S quency, for instance, to the output ofan amplifier Sllghllly enlarged and has mounted therein two Si which amplifies sound-frequency oscillations imheavy metallic blocks 33 and 34 which are D1 ECI- C!) pressed by a microphone exposed to the sound. alloly rlgldly secured wlllllln the oaslng during the Within the vibrator casing I6 is mounted a molding opel'alllon- The two blocks 33 34 are n- Vibrator unit 2g show-n in detail in Figs. 7 and 8 sulated from each other by an insulating rib 35 It comprises a pair of at longitudinal plates or Which fOTmS a Dart 0f the body 0f the casing.

c5 strips 2| and 22 of Rochelle salt crystal, each The casing chamber 3l has at its downward end ci strip being approximately 11/2 long, wide, an extension formed between the blocks 33 and and%"thick. These crystal strips are made from 34 to receive the lower end of the fiat crystal a Rochelle salt crystal-plate, like plate l0 shown unit, the height of the extension being slightly in Fig. 1, by cutting therefrom the strip along an less than the thickness of the assembled crystal 'I Il axis inclined 45 to the optical axis, 'as indicated unit 20. Before insertion into the chamber of T'l in Fig. 2 by the dotted line 2|. Such strips cut the casing, the crystal unit 20 is enclosed in a thin from a Rochelle salt crystal, with the plane surinsulating enclosure 38,`preferably of a yieldable faces thereof perpendicular to the electric axis, and moisture-tight substance, such as rubber. and extending longitudinally under an angle of The enclosure 38 prevents contamination of the 45 against 'the optical axis, will expand in longlcrystal by handling andby body secretions and 75 insulates the electrode layers against external contact. By making the enclosure 38 of a thin resilient rubber, such as dental dam rubber, there is also provided a yielding layer which distributes sudden applied vforces over the surface of the crystal and prevents breaking thereof.

The lower end of the crystal unit 2li which rits into the cavity extension formed between the blocks 33 and 34 is clamped in place by an insulating clamping plate of fibre, for instance, which is molded in within the lower end of the casing cover 32, and is clamped against the block by means of clamping screws 4l. Additional small screws 43 serve to hold the upper portion of the casing cover 32 firmly clamped to the casing, as shown in Fig. 5. The portion of the casing chamber 3| extending above the clamping blocks 33 and 34 is somewhat wider and provides sufcient space opposite the 'flat outer sides of the casing for inserting two layers 44 and 45 of a soft yielding material, such as sponge rubber. These rubber bodies offer only negligible resistance against the vibratory movement of the upper portion of the vibrator unit 20 and act merely as cushions. Their use is, however, not necessary for the operation of the device.

At the upper end of the casing cover 32 near the an opening` 48 having at its rear end a supporting iiange 49 bearing against the upper end of the vibrator The button 48 is guided in the opening the opening, the collar being preferably of rubber and touching lightly the surface of the button 48 to permit its free movement therein. The outer end of the button forms a contact surface 5| which acts against the bone structure 52 of the head of the listener, for instance, against the mastoid bone as shown 'in Fig. 4.

'I'he head ban l1 which may, for instance, be inthe form of wire or a thin strip of resilient material has at its end a flat portion 55 attached to a U-shaped member 56 having ilat arms 51 iitting into a channel member 5l secured to the side walls of the casing '|6, for carrying the casing and pressing the contact portion 5l of the vibrator button against the bone structure.

The electrical circuit connections to the elec'- trode sheets of the crystal unit are made by soldering the ends of the contact members 29 and 30 to the two blocks 33 and 34 as indicated in Fig. 6, thesestrips being also held against the block by the pressure of the clamping plate 40. -Downward openings 6| are provided in the rear portions of the blocks 33 and 34 into which the ends of the two lead conductors i8 are inserted and clamped by means of screws 62 threaded from the rear side of the clamping blocks.

Upon application of. an electric sound frequency oscillation source to the crystal terminals 23 and 30, through the cord I8, a vibratory movement in a direction perpendicular to the plane of the crystals is imparted clamped between the clamping members 33, 34 and the clamping plate 40. lng the lower end of the crystals mass to have suilicient inertia t secure imparting oi the required vibratory power to the bone structure. The rubber layer surrounding the lower end of the vibrator unit 20 serves as a cushioning means for permitting limited local motion of the crystal and equalizes the pressure ex ercised by the clamping surfaces on the crystal.

are made of large to the portion of the vibrator unit extending above the lower end The sponge rubber cushions 44, prevent excessive bending of the crystal by exterior pressure on the button or the casing, thus guarding against breakage of' the crystal. The rubber sleeve surrounding the button prevents rattling of the serves to seal the casing and provide an additional enclosure of the interior crystal, protecting it against moisture and body excretions The casing and enclosure 38 also isolate the u ser from the parts in the interior oi the casing which are under potential. y

The wall of the casing opposite the contact button 5l should be sufficiently spaced to permit the crystal to vibrate freely within the range imparted by the impressed electrical potentials. A definite stop should be provided about 5 to 10 mils on the rear side ofv the vibrator crystals to prevent excessive deformation of the crystal due to a large external force applied against the button.

In the arrangement shown in Figs. 5 and 6, special provision has been made for preventing deflection of the vibrator unit from its normal position whenrthe vibrating casing is applied against the body and an initial pressure is exerted by the bone structure on the button tending to push the upper end of the vibrator unit in rearward direction. To this casing wall opposite the button is provided with a circular sleeve 65 within which is slidably mounted a cup-shaped piston` 66 which is held pressed inwardly against the rear surface of the vibrator unit by a helical spring 61 held within the interior of the sleeve by a cap threadedly mounted over the opening of the sleeve 65 to permit regulation of the pressure acting on the'piston 66. This pressure is so adjusted that the force exerted by the piston 6B on the rear side of the vibrator unit is equal to the force with which the button 48 is pressed against the bone structure. By this arrangement the vibrator unit i`s held in its'normal untensioned position when the button is held pressed against the body, while no potential is applied to the crystal electrodes.

Instead of the mechanicalarrangement for compensating the pressure exercised on pressing the button against the bone structure, an electrica-l compensation of this effect maybe obtained by applying to the terminals of thecrystal vibrator unit a direct current biasing potential tending to bending strain equal and opposite to the force which the bone structure exercises on the button.

The vibratorl device described above is characterized by a number of features which particularly adapts it for the special use as a bone-conduction instrument. By using a bender-type vibrating unit, it is possible to small inconspicuous structure sufficient vibratory power to impart to the listener enough vibratory energy for inducing satisfactory hearing sensa,- tions inhis auditory center and make him-hear like a normal person. unit at one end in a heavy clamp, eicient transfer of the vibrations to the bone structure isimade possible. By completely enclosing the vibrating unit in a Waterproof resilient enclosure, moisture and secretions are kept away from' the crystal lstructure and the crystal electrodes are protected against contact. By using a relatively rigid casing around the vibrator unit, damage to the crystal by external forces is prevented without impairing efficient transmission of vibrations 68 that is develop within a By clamping the crystal end the part or the to the bone structure. The heavy clamp supplies sucient inertia for .developing Vibratory power necessary for imparting the vibratory energy to the bone structure. By the special dimensioning of the interior space within the enclosing casing, there are obtained free oscillations of the crystal within the range of motion imparted to it by the impressed electrical oscillations, While excessive deflection of the vibrator unit that might cause its breakage is removed.

Because of the requirement that the vibrator shall be inconspicuous, the crystal vibrator unit must be of very little weight of the order of 2 to 3 grams. The head structure to which it must impart the vibrations weighs several kilograms. Although a vibratorunit of such small mass will transmit suicient vibratory energy to the head structure at frequencies above several thousand cycles, the amount of energy transmitted by the crystal at low frequencies is negligible. The additional inertia mass provided by the clamps 33 and 34 extends this range downwardly to frequencies of several hundred cycles and below. Since only a small mass, of about 15 grams, of disposable weight can be added without too much enlarging the structure of the vibrator, the mass is concentrated at the lower end of the vibrator unit opposite the point where it is coupled to the head. Because of the relatively large mass of the head coupled tothe upper end ofthe crystal vibrator unit and the provision of the weight of the relatively heavy clamp at the lower end of the unit, eiective utilization of the limited mass available is obtained.

In Figs. 9 and 10 there is shown another embodiment of the invention in which the use of a button for transmitting the vibrations is completely avoided. A bender vibrator unit like that shown in connection with Figs. and 6 is mounted Within a special casing 10 having a lower portion 1I like the lower portion of casing of Figs. 5 and 6 with a pair cf blocks 12 and 13 to which the vibrator unit 14 is clamped by means of a vibrator plate 15 constituting a part of a cover member 16 of the lower casing portion. The vibrator unit 14 is firmly held in this lower casing portion and the unclamped upper portion of the vibrator unit is vibrated upon application of electric soundfrequency oscillations to the electrode surfaces of the vibrator unit.

Directly above, and as a continuation of the lower-,casing portion, is mounted an upper casing portion 18 made of metal or other light material, and compietely surrounding the upper portion of the vibrator unit 14 so that the entire unit is enclosed. At its lower side. walls the upper casing portion 18 has hinges 19 which overlap the spaces and provides a resilient ller in the spaces between the lower edges of the upper casing and the upper edges oi the sealing the spaces therebetween.

Near the upper end of the casing 18, there arel ture, indicated at 85, ,by means of a head band l1, as shown in Fig. 4, the end of the head band having a at end portion 86 which ts into a at channel 81 provided on the rear side of the lower casing portion.

The vibrator device of Figs. 9 and 10 is of simple construction and gives thorough protection to the Rochelle salt crystal vibrator unit. Damage to the crystal body by excessive bending is prevented by the relatively short gap between the edges of the upper casing portion and the lower casing portion, these edges limiting the oscillatory movement of the upper casing member to a range at which the vibrator unit 14 cannot be excessively strained.

In the vibrator device shown in Figs. 11 and 12, a bender Vibrating unit 9D is mounted in a casing 9| in a way similar to the vibrator of Figs. 5 and 6. However, instead of a button for transmitting the vibrations from the vibratory unit 90 to the bone structure, the casing cover 92 has a large rectangular opening 93 in its upper part, this opening having mounted therein a rectangular reed member 94, the lower end of which is secured, as by molding, within the lower part of the casing cover. The reed member 94 substantially completely encloses the opening in the casing wall, and the space 95 between the reed member and the front surface of the vibrator, as Well as the rear space 96 of the casing, are filled with sponge rubber permitting free vibration of the reed, while sealing the interior space. A vibration transmitting block S1 extending between the reed member 94 and the vibrator unit 9D Atransmits the vibratory motion of the vibrator unit to in the rear side of the casing.

In all of the foregoing arrangements, the vibrator unit is completely protected; being entirely the applied potentials. The unit is extremely small, its height being less than 2 inches, its width being only about 1/2 of an inch, and its thickness slightly over 1A of an inch.

Such vibrator devices may be made to directly expose a portion of the crystal vibrator unit and permit its direct application to the bone structure. Thus, for instance, the arrangement as shown in Fig. 5 may be modified by leaving on' the front portion of the upper end of the casing i6 to expose the front part of the upper end of the crystal vibrator unit and permit its direct handle may also be provided with a hollow portion |02 arranged to receive and clamp the lower `end of the vibrator casing and increase the mass and the inertia thereof.

The invention is not limited to the details of construction and arrangement described in con- 75 Fig. 13, the lorgnette tion of said vibrator unit acume? nection withv the exemplications thereof, as many modications will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the' scope of the invention. l

1. In a piezo-electric hearing-aid bone-vibrator device, a piezo-electric vibrator unit of inconspicuous size, electrode means for impressing electric sound-,frequency oscillations on the piezo-electric substance of said vibrator unit to produce a vibratory motion of said unit, a floating support of substantial mass holding a portion'of said unit, means for coupling a portion of said vibrator unit to hearing-inducing bone structure of a person for imparting thereto hearing-inducing vibratory energy by the vibratory motion of said unit, and an enclosure extending IrofmA said support enclosing the piezoelectric substance of said unit.

2. In a piezo-electric hearing-aid bone-vibrator device, a piezo-electric vibrator unit of inconspicuous size, electrode means for impressing electric sound-frequency oscillations on the piezo-electric substance of said vibrator unit to produce a vibratory bending motion of said unit, a iioating support of substantial mass holding a portion of said unit, means for coupling a porto hearing-inducing bone structure of a person for imparting thereto hearing-inducing vlbratory energy by the vibratory motion of said unit, and an enclosure extending from 'said support enclosing the piezoelectric substance of said unit.

3. In a hearing-inducing bone-vibrator device actuated by electric sound-frequency oscillations for imparting corresponding mechanical vibrasaid unit.

tions to a bone structure of a person and inducing by bone-'conduction corresponding sounds in his auditory center, a piezo-electric vibrator unit of small size suitable for inconspicuous Wear, conducting electrode layers in said unit for raceiving electric sound-frequency oscillations and imparting by piezo-electric action mechanical vibrations corresponding to said oscillations to said unit, a floating support of substantial mass holding one portion of said vibrator unit, means for coupling another portionof said vibrating unit spaced from the supported portion to hearinginducing bone structure of `a person in a position at which said v1brator unit will impart to said bone structure an amount of vibratory power sufcient for imparting to ysaid person satisfactory hearing, and a yieldable enclosing coating direct contact on said vibrator unit Apreventing between said electrode layers andl the exterior surface of said bone structure.

4. In a piezo-electric hearing-aid bone-vibrator device, a piezo-electric vibrator unit of inconspicuous size, electrode means for impressing electric sound-frequency oscillations on the piezo-electric substance of said vibrator unit to produce a vibratory bending motion of said unit, a iloating su port of substantial mass holding a portion of said unit, means for coupling a porpcrt to hearing-inducing bone structure of a person for imparting thereto hearing-inducing vibratory energy by the vibratory motion of said unit, and an enclosure extending from said support enclosing the piezo-electric substance of SIDNEY YOUNG WHITE. 

